Many lighting circuits enable a user, or an external control circuit, to provide a dimming signal. The lighting circuit is typically required to adjust the ultimate light intensity responsive to the dimming signal. Such light circuits are useful for both general lighting and backlighting applications, such as in monitors and televisions.
Unfortunately, there is no standard for dimming signals, and thus each system designer is free to select the dimming method of their choice. At present, there exists in wide use a few typical dimming signal types, without limitation:                a. An analog signal, whose value is representative of the desired dimming level, i.e. the signal may range over a plurality of values, with the highest value representing the maximum dimming, i.e. minimum luminance;        b. An analog signal, whose value is representative of the desired luminance, i.e. the signal may range over a plurality of values, with the highest value representing the minimum dimming, i.e. maximum luminance; and        c. A pulse width modulated (PWM) signal whose duty cycle represents the desired dimming level, with a duty cycle of 1 typically representing the maximum luminance.It is to be noted that the above list is not meant to be limiting in any way, and other dimming schemes, including an AC signal whose average of the absolute value is representative of the desired luminance may be provided without exceeding the scope. The analog signal may be directly provided, or alternatively the lighting circuit may be required to provide a driving circuitry to be attached to a variable resistance, the variable resistance in cooperation with the driving circuitry thus providing the analog signal.        
As a result a lighting circuit must be designed and inventoried for each potential dimming type, thus increasing cost. Alternately, a plurality of leads must be supplied for a signal lighting circuit, each of the plurality of leads associated with a target dimming type signal.
What is desired, and not supplied by the prior art, is a lighting circuit with a single dimming input lead suitable for use with multiple dimming type signals.